Rotary blowers of the backflow-type, particularly Roots-type blowers are characterized by noisy operation. Roots-type blower noise may be roughly classified into two groups: solid borne noise caused by rotation of timing gears and rotor shaft bearings subjected to fluctuating loads, and fluid borne noise caused by fluid flow characteristics such as rapid changes in fluid velocity. The invention of this application is concerned with solid borne noise caused by timing gear rattle.
The timing gears of the Roots-type blowers, such as the blower disclosed in U.S. Pat. No. 4,638,570, are known to produce an objectionable gear rattle when the meshed teeth of the gears are substantially unloaded. Such an unloaded condition occurs during non-supercharging, low engine speed operation.